This invention concerns a dental implant used as an artificial tooth root for holding a dental prostheses.
Dental implant typically comprises an elongated pin inserted into a hole drilled into the bone beneath a patient's gum tissue. The implants have taken two basic forms, a smooth cylindrical form which is press fit into the drilled hole and bonded to the osseous tissues to be held securely; and, a threaded form which is rotated into the hole which is suitably prepared by special bone tapping techniques.
The geometry of a threaded implant is such that it is immediately securely interlocked with the surrounding bone, the thread form when advanced into the hole creates excessive stresses in the bone tissue, which can cause the bone tissue to react and recede over time, leading to a loss of securement of the implant.
A threaded hole in the top of the implant is used for attachment of the prosthesis to the implant, and removal of a threaded attachment can sometimes result in loosening of the implant by unintended unscrewing of the implant threads when the attachment is loosened.
The press fit cylindrical form of the implant is simpler to install and has more bone attachment due to the absence of stress risers, but is less securely held in the bone tissue at the time that the implant is first driven into the hole since there is no positive mechanical interlock. The threaded form also has the advantage of having a greater surface area in contact with the bone, at least initially, to further increase the bonding forces.
Variations of these two basic forms have been devised, including a threaded form with the addition of a long pitch helical groove and through holes for receiving bone fragments packed into the groove to promote the growth of bone tissue into the groove for increased long term holding ability for the implant, as described in U.S. Pat. No. 5,676,545 issued on Oct. 14, 1997 for a "Method and Apparatus for Implantation".
U.S. Pat. No. 5,762,499 issued on Jun. 9, 1998 for a "Dental Root Implant" describes a press fit geometry in which the implant body is tapered and has circumferential grooves for receiving bone growth. U.S. Pat. No. 5,195,892 issued on May 23, 1993 for a "Bone-Integrated Dental Implant System" describes longitudinal grooves in the implant sides to promote interlocking bone growth.
U.S. Pat. No. 5,269,686 issued on Dec. 14, 1993 for a "Threaded Drivable Dental Implant" describes a long pitch rounded thread on an implant body which is drivable in the drilled hole and which resists loosening when an attachment screw is removed.
It is the object of the present invention to provide a dental implant which has the advantages of both the press fit and threaded forms while minimizing the disadvantages of each.